Add 1D Fast Fourier Transform FFT NKI kernel implementation

[jimburtoft]

Description of changes:

• Hardware-accelerated 1D FFT using Tensor Engine
• Supports arbitrary heights and power-of-2 widths (128-4096)
• Radix-2 Cooley-Tukey algorithm with 128-point DFT base case
• High accuracy (< 0.003% error vs NumPy)
• Comprehensive unit tests with performance benchmarks"

Testing:

Just covered by function specific unit testing.

Pull Request Checklist

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• [ x] I have tested locally that all the tests pass
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